Method for producing lead-base alloy grid for lead-acid battery

ABSTRACT

The present invention relates to a method for producing a lead-base alloy grid for lead-acid battery having excellent mechanical strength, corrosion resistance and growth resistance, including two-step heat treatment of a Pb—Ca—Sn alley grid containing 0.06% by mass or less of calcium, the first heat treatment being conducted at a temperature of 40° C. to 110° C., the second heat treatment being conducted at a temperature of 90° C. to 140° C., and the first heat treatment being conducted at a lower temperature than the second heat treatment.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Continuation Application of PCT Application No.PCT/JP2008/070244, filed Oct. 30, 2008, which was published under PCTArticle 21(2) in English.

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2007-287121, filed Nov. 5, 2007,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for producing a lead-basealloy grid for lead-acid battery, the grid being useful for automotivebatteries, VRLA batteries, industrial cycle use batteries, ventedbatteries and VRLA batteries for standby, cylindrical wound batteries,and the grid having excellent mechanical strength, corrosion resistance,and growth resistance.

2. Description of the Related Art

Recently, as the increase of automobile trims and the reduction ofuseless spaces, engine rooms, in which lead-acid batteries forautomobiles are placed, become places of a higher temperatureenvironment than before. In addition, lead storage batteries are alwaysin the state of overcharge, so that have shorter life than otherlead-acid batteries. Further, Pb—Ca alloy grid introduced with theintention of obviating the necessity of maintenance tend to cause theproblem of growth, which is deformation of the anode grid by corrosionor elongation, and thus have shorter life than conventional ones.

These problems such as corrosion and growth can be resolved bydecreasing the Ca content in the Pb—Ca alloy substrate, but the decreaseof the Ca content results in the decrease of Ca-containing intermetalliccompounds such as Pb₃Ca and (Pb,Sn)₃Ca to cause the deterioration of thegrid strength and deformation of the grid during pasting of an activematerial paste.

Then, it was attempted to decrease the Ca content in a Pb—Ca—Sn alloy,for example, from 0.09% by mass to 0.06% by mass, and then 0.04%, andcompensate the loss with Ba or Ag thereby improve the strength. However,sufficient improvement of the mechanical strength was not achieved.

A method for improving the strength of a Pb—Ca—Sn alloy through naturalaging is disclosed in R. D. Prengaman, J. Power Sources 95 (2001) 226.It is shown that an alloy containing 0.065% by mass of Ca requires agingtreatment for 24 hours, and an alloy containing 0.045% by mass of Carequires aging treatment for 14 days, and an alloy containing 0.025% bymass of Ca requires aging treatment for 60 days to achieve intendedhardness. However, the method requires too much time for natural agingof an alloy containing lower Ca, and is thus insufficient to bepractical.

Jpn. PCT National Publication No. 2004-527066 discloses a method forsubjecting a Pb—Ca—Sn—Ag alloy containing 0.02 to 0.06% by mass of Ca toartificial aging at 100° C. for 3 hours. WO03/088385A1 discloses amethod for subjecting a Pb—Ca—Sn—Ba—Ag alloy containing 0.02 to 0.05% bymass of Ca to heat, treatment at a temperature of 80 to 150° C. for aperiod of 0.5 to 10 hours within 1000 hours after casting the grid.However, these methods involve a wide range of mechanical variation, andthe artificial aging may be ineffective. Therefore, these methods haveproblems with stability of plant operation.

In order to improve the mechanical strength of a Pb—Ca—Sn alloy gridcontaining a decreased amount of Ca, the inventors performed thedifferential scanning calirimetry of a Pb—Ca—Sn alloy, and made a minuteinvestigation of the result. As a result of this, a broad region over awide range was found in a temperature range lower than the range forknown peaks, the region is likely attributable to the heat generationprocess. The region is due to the deposition reaction of the precursorto be the deposit nuclear, and the deposit is considered to grow fromthe precursor as the nuclear.

On the basis of the estimation, the inventors conducted the first heattreatment at low temperature thereby promoting the precursor formation,and then conducted the second heat treatment at high temperature to growthe deposit. As a result of this, the resultant Pb—Ca—Sn alloy gridexhibited improved mechanical strength.

Heretofore, artificial aging such as heat treatment, is regarded asaccelerated natural aging for slowly depositing intermetallic compoundssuch as Ph₃Ca and Sn₃Ca from oversaturated solid solution by coolingafter casting. The precursor herein is considered to be equivalent tothe GP zone or intermediated phase deposit in an aluminum alloy.However, there is no report evidently showing the presence of theprecursor in a lead alloy.

BRIEF SUMMARY OF THE INVENTION

The present invention is intended to provide a lead-base alloy grid forlead-acid battery with excellent mechanical strength, corrosionresistance, and growth resistance.

An aspect of the present invention is a method for producing a lead-basealloy grid for lead-acid storage battery, including two-step heattreatment of a Pb—Ca—Sn alley grid containing 0.06% by mass or less ofcalcium. The first heat treatment is conducted at a temperature of 40°C. to 110° C., and the second heat treatment is conducted at atemperature of 90° C. to 140° C. The first heat treatment is conductedat a lower temperature than the second heat treatment.

According to the present invention, the Pb—Ca—Sn lead-base alloy gird issubjected to two-step heat treatment, wherein the first neat treatmentforms a precursor to be the deposit nuclear, and the second heattreatment grows the precursor into a deposit. Accordingly, thedeposition finely and quickly proceeds, and the resultant substrate hasa high strength in spite of the Ca content that is as low as 0.06% bymass or less, and deformation during pasting of an active material isprevented. In addition, the Ca content in the Pb—Ca—Sn alloy used in thepresent invention is so low that the alloy has excellent corrosionresistance and growth resistance.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method for producing a lead-basealloy grid for lead-acid storage battery including two-step heattreatment of a Pb—Ca—Sn alloy grid containing 0.06% by mass or less ofcalcium, the first heat treatment being conducted at a temperature of40° C. to 110° C., the second heat treatment being conducted at atemperature of 90° C. to 140° C., and the first heat treatment beingconducted at a lower temperature than the second heat treatment.

In the present invention, the reason that the Ca content in the Pb—Ca—Snlead-base alloy is defined as 0.06% by mass or less is that corrosionresistance and growth resistance of the grid are insufficient if the Cacontent exceeds 0.06% by mass. The Ca content is even more preferablyless than 0.05% by mass.

Regarding the heat treatment temperature, the reason that the first heattreatment temperature is defined as from 40° C. to 110° C. is that theformation of the precursor is not accelerated at temperatures lower than40° C., and substantially no precursor is formed at temperatures higherthan 110° C. If the heat treatment temperature is lower than 40° C. orhigher than 100° C., the growth of the deposit by the second heattreatment and resultant strength improvement effect are not sufficientlyachieved. The behavior of the precursor formation is substantiated bythe result of the measurement of differential scanning calorie.

In the first heat treatment, if the heat treatment time is shorter than0.5 hours, the formation of the precursor is insufficient, so that thestrength improvement effect is insufficient. The period of the firstheat treatment is preferably 0.5 hours or more. The heat treatment timemay be appropriately adjusted in consideration of productivity so as notto be shorter than 0.5 hours, but if the period is 15 hours or more, theprecursor may partially grow into a coarse deposit to show an overagedstate. Accordingly, the first heat treatment time is preferably shorterthan 15 hours.

In the present invention, the reason that the second heat treatmenttemperature is defined as from 90° C. to 140° C. is that the growth ofthe deposit is slow at temperatures lower than 90° C., and the depositexcessively grows at temperatures higher than 140° C. In both cases,sufficient mechanical strength cannot be achieved. If the second heattreatment time is shorter than 0.5 hours, the growth of the deposit isinsufficient, and if longer than 10 hours, the deposit excessivelygrows. In both cases, sufficient mechanical strength cannot be achieved.Accordingly, the second heat treatment time is preferably from 0.5 hoursto 10 hours.

In the present invention, the first heat treatment is conducted at alower temperature than the second heat treatment. The reason for this isthat the precursor is not sufficiently formed if the first heattreatment temperature is higher than the second heat treatmenttemperature, and thus enhancement of the deposition by the second heattreatment is not sufficiently achieved. The strength improvement effectcan be increased by conducting natural aging before the first heattreatment. The period of natural aging is preferably 0.5 hours or more,and a period about 3 hours is sufficient. Even if the period is extendedlonger, the effect of the natural aging will not be improved. Thus, thepreferable period is 0.5 hours or more, and further in terms of theproductivity, a period of about 3 hours is appropriate.

In the present invention, the effect of two-step heat treatment onstrength improvement is particularly good for a lead-base alloycontaining 0.02% by mass or more and less than 0.05% by mass of calcium,0.4% by mass or more and 2.5% by mass or less of tin, 0.005% by mass ormore and 0.04% by mass or less of aluminum, and 0.002% by mass or moreand 0.014% by mass or less of barium, the remainder being composed oflead and unavoidable impurities.

In the lead-base alley of the present invention, Ca enhances themechanical strength of the alloy. If the Ca content is less than 0.02%by mass, the effect is insufficient, and if 0.05% by mass or more,corrosion resistance is impaired. In the alloy of the present invention,the Ca content is preferably from 0.03% to 0.045% by mass.

In the alloy of the present invention, Sn improves the flow of moltenalloy and mechanical strength of the lead-base alloy. If Sn oozed out ofthe grid-active material interface is doped by the corrosion layer, theelectrical conductivity of the grid-active material interface isimproved by the semiconductor effect. If the Sn content is less than0.4% by mass, the effect is insufficient and corrosion resistancedeteriorates. If the Sn content is more than 2.5% by mass, the crystalgrain of the lead-base alloy coarsen, which may result in corrosion ofgrain boundaries beyond apparent corrosion. The Sn content is morepreferably from 0.6% to 2.5% by mass.

Al suppresses the loss of Ca and Ba caused by oxidation of molten metal.If the Al content is less than 0.005% by mass, the effect isinsufficient, and if more than 0.04% by mass, Al tends to deposit asdross to deteriorate flow of molten alloy.

Ba improves the mechanical strength and corrosion resistance of thelead-base alloy. If the Ba content is less than 0.002% by mass, theeffect is insufficient, and if more than 0.014% by mass, the corrosionresistance rapidly deteriorates. The Ba content is more preferably from0.002% to 0.010% by mass.

When the lead-base alloy contains at least one selected from the groupconsisting of Ag, Bi, and Tl in an appropriate amount, the alloy hasimproved mechanical strength or creep properties (growth resistance) athigh temperatures. Ag markedly improves mechanical strength, inparticular high temperature creep properties. If the Ag content is lessthan 0.005% by mass, the effect is insufficient, and if more than 0.070%by mass, cracking may occur during casting. The Ag content is morepreferably from 0.01% to 0.05% by mass. Bi contributes to theimprovement of mechanical strength. The effect is lower than than of Ag,but Bi is economical because it is less expensive than Ag. If the Bicontent is less than 0.01% by mass, the effect is insufficient, and ifmore than 0.10% by mass, corrosion resistance deteriorates. The Bicontent is more preferably from 0.03% to 0.05% by mass. Tl contributesto the improvement of mechanical strength. Tl is inexpensive and thuseconomical. If the Tl content is less than 0.001% by mass, the effect isinsufficient, and if more than 0.005% by mass, corrosion resistancedeteriorates. The Tl content is more preferably from 0.005% to 0.05% bymass.

In the present invention, the lead-base alloy grid is preferably made bygravity casting, continuous casting, die casting, or rolling. Any ofthese processes produces a lead-base alloy grid having excellentmechanical strength, corrosion resistance, and growth resistance. Thelead-base alloy of the present invention exhibits the same effect whenit is used for lead components other than substrates.

Example 1

Each of the molten metals of the lead-base alloys (A) to (H) having thecompositions shown in Table 1 was gravity-cast under a book mold systemto make strap samples having a length of 200 mm, a width of 15 mm, and athickness of 1.5 mm at a rate of 15 pieces per minute. The samples weresubjected to two-step heat treatment thereby producing lead-base alloygrids for lead storage battery. The first and second heat treatmentswere conducted under the conditions defined in the present invention.The period of natural aging after casting to the initiation of heattreatment was variously changed. Each of the resultant lead-base alloygrids was measured for its hardness using a micro Vickers indenter underthe conditions of a load of 25 gf and a load retention time of 15seconds. Those exhibited a hardness of 12 or more were evaluated ashaving excellent mechanical strength.

As comparative examples, lead-base alloy grids for lead-acid batterywere made in the same manner as Example 1, except that the conditions ofthe first heat treatment were different from those defined in thepresent invention, and the girds were measured for their hardness toexamine their mechanical strength in the same manner as Example 1. Theresults of Examples and Comparative Examples are shown in Table 2.

TABLE 1 Alloy Ca Sn Al Ba Ag Bi Tl A 0.055 1.0 0.008 — — — — B 0.040 1.00.008 — — — — C 0.040 1.0 0.008 0.007 — — — D 0.035 1.0 0.010 0.007 — —— E 0.040 1.0 0.010 0.007 — — — F 0.040 1.0 0.010 0.007 0.02 — — G 0.0401.0 0.010 0.007 — 0.03 — H 0.040 1.0 0.010 0.007 — — 0.01 Note) unit: %by mass

TABLE 2 Heat treatment conditions Example No. Alloy Natural aging timeFirst step Second step Hardness Example 1 1 A 1 h 70° C. × 1 h 120° C. ×3 h 17 2 B 1 h 70° C. × 1 h 120° C. × 3 h 13 3 C 1 h 70° C. × 1 h 120°C. × 3 h 15 4 D 1 h 70° C. × 1 h 120° C. × 3 h 14 5 E 1 h 70° C. × 1 h120° C. × 3 h 18 6 F 1 h 70° C. × 1 h 120° C. × 3 h 19 7 G 1 h 70° C. ×1 h 120° C. × 3 h 20 8 H 1 h 70° C. × 1 h 120° C. × 3 h 20 9 E 1 h   40°C. × 0.5 h 120° C. × 3 h 16 10 E 1 h 40° C. × 1 h 120° C. × 3 h 17 11 E1 h 50° C. × 1 h 120° C. × 3 h 18 12 E 1 h 90° C. × 1 h 120° C. × 3 h 1913 E 1 h 110° C. × 1 h  120° C. × 3 h 18 14 E 1 h 70° C. × 1 h  90° C. ×3 h 17 15 E 1 h 70° C. × 1 h 140° C. × 3 h 16 16 E 0.1 h   70° C. × 1 h120° C. × 3 h 12 17 E 0.5 h   70° C. × 1 h 120° C. × 3 h 18 18 E 1 h 70°C. × 1 h 120° C. × 3 h 20 19 E 3 h 70° C. × 1 h 120° C. × 3 h 21 20 E 4h 70° C. × 1 h 120° C. × 3 h 21 21 E 7 h 70° C. × 1 h 120° C. × 3 h 21Comparative 22 E 1 h 30° C. × 1 h 120° C. × 3 h 11 Example 1 23 E 1 h120° C. × 1 h  120° C. × 3 h 11 Comparative 24 E 1 h — 120° C. × 3 h 10Example 2

As is evident from Table 2, the alloy grids of No. 1 to No. 21 accordingto the example of the present invention had hardness of 12 or more,indicating their excellent mechanical strength. The result is due tothat the first and second heat treatments were conducted under theconditions defined in the present invention, so that the precursor of aCa-containing deposit successfully occurred and grew to a deposit. Theresults shown in Table 2 indicate the effect of Ca (comparison betweenNo. 1 and No. 2), the effect of Ba (comparison between No. 2 and No. 3),and the effects of Ag, Bi, and Tl (No. 6 to No. 8) on mechanicalstrength.

The evaluations of No. 16 to 21 shown in Table 2 indicate that hardnessincreased as the increase of the natural aging time up to 3 hours, butthe hardness reached a level of saturation and did not increasethereafter. It should be noted here that the period of natural aging ispreferably 0.5 hours or more, and a period about 3 hours is sufficient.Even if the period is extended longer, the effect of the natural agingwill note be improved. Thus, the preferable period is 0.5 hours or more,and further in terms of the productivity, a period of about 3 hours isappropriate.

On the other hand, No. 22 and 23 of Comparative Example 1 exhibitedinferior mechanical strength because they were subjected to the firstheat treatment at a tempera cure not defined in the present invention.No. 24 also exhibited inferior mechanical strength because it was notsubjected to the first heat treatment.

Example 2

Each of the samples of the present invention (No. 1 to 21 of Example 1),and a known lead-base alloy grid (Pb: 0.07% by mass, Ca: 1.0% by mass,Sn: 0.01% by mass, Al alloy) were examined for corrosion resistance andhigh temperature creep properties. In order to examine corrosionresistance, the sample was anodized in a dilute sulfuric acid aqueoussolution having a specific gravity of 1.280 (20° C.) and a temperatureof 60° C. for 720 hours at a constant potential of 1350 mV (vs, Hg₂SO₄),and then the corrosion weight loss for a unit area of the sample wasmeasured. The corrosion weight loss of the samples of the presentinvention was 20 mg/cm² or less, indicating their excellent corrosionresistance.

In order to examine high temperature creep properties, the sample wassubjected to a load of 16.5 MPa, then heated to 100° C., and the timeuntil the rupture of the sample was measured. As a result of this, thesamples of the examples of the present invention took 25 hours or moreuntil they ruptured, indicating their excellent high temperature creepproperties (growth resistance).

On the other hand, the Ca content in the known lead-base alloy was ashigh as 0.07% by mass, so that the corrosion weight loss was 35 mg/cm²,and the time until the rupture of the sample was 14 hours, indicatingthat the substrate has inferior corrosion resistance and hightemperature creep properties (growth resistance).

1. A method for producing a lead-base alloy grid for lead-acid battery,comprising heat treatment of a Pb—Ca—Sn alloy grid containing 0.06% bymass or less of calcium, the hear treatment is conducted in two steps,the first heat treatment being conducted at a temperature of 40° C. to110° C., the second heat treatment being conducted at a temperature of90° C. to 140° C., and the first heat treatment being conducted at alower temperature than the second heat treatment.
 2. The method forproducing a lead-base alloy grid for lead-acid battery of claim 1,wherein the first heat treatment is conducted for a period of 0.5 hours,and the second heat treatment is conducted for a period of 0.5 hours to10 hours.
 3. The method for producing a lead-base alloy grid forlead-acid battery of claim 1, wherein natural aging is conducted beforethe first heat treatment.
 4. The method for producing a lead-base alloygird for lead-acid battery of claim 2, wherein at least natural aging isconducted before the first heat treatment.
 5. The method for producing alead-base alloy grid for lead-acid battery of any one of claims 1 to 4,wherein the Pb—Ca—Sn alloy comprises 0.02% by mass or more and less than0.05% by mass of calcium, 0.4% by mass or more and 2.5% by mass or lessof tin, 0.005% by mass or more and 0.04% by mass or less of aluminum,and 0.002% by mass or more and 0.014% by mass or less of barium, theremainder being composed of lead and unavoidable impurities.
 6. Themethod for producing a lead-base alloy grid for lead-acid battery anyone of claims 1 to 4, wherein the Pb—Ca—Sn alloy comprises 0.02% by massor more and less than 0.05% by mass of calcium, 0.4% by mass or more and2.5% by mass or less of tin, 0.005% by mass or more and 0.04% by mass orless of aluminum, 0.002% by mass or mere and 0.014% by mass or less ofbarium, and at least one element selected from the group consisting of0.005% by mass or more and 0.070% by mass or less of silver, 0.01% bymass or more and 0.10% by mass or less of bismuth, 0.001% by mass ormore and 0.05% by mass or less of thallium, the remainder being composedof lead and unavoidable impurities.
 7. A method for producing alead-base alloy grid for lead-acid battery, comprising heat treatment ofa Pb—Ca—Sn alloy grid containing 0.06% by mass or less of calcium, theheat treatment being conducted in two steps, the first heat treatmentbeing conducted at a temperature of 40° C. to 110° C., the second heattreatment being conducted at a temperature of 90° C. to 140° C., thefirst heat treatment being conducted at a lower temperature than thesecond heat treatment, and the lead-base alloy grid for lead-acidbattery being made under gravity casting system, die casting system,continuous casting system, or rolling system.
 8. A method for producinga lead-base alloy grid for lead-acid battery, comprising heat treatmentof a Pb—Ca—Sn alloy substrate containing 0.06% by mass or less ofcalcium, the heat treatment being conducted in two steps, natural agingbeing conducted before the first heat treatment, the first heattreatment being conducted at a temperature of 40° C. to 110° C., thesecond heat treatment being conducted at a temperature of 90° C. to 140°C., the first heat treatment being conducted at a lower temperature thanthe second heat treatment, and the lead-base alloy grid for lead-acidbattery being made under gravity casting system, die casting system,continuous casting system, or rolling system.
 9. A method for producinga lead-base alloy grid for lead-acid battery, comprising heat treatmentof a Pb—Ca—Sn alloy substrate containing 0.06% by mass or less ofcalcium, the heat treatment is conducted in two steps, the first neattreatment being conducted at a temperature of 40° C. to 110° C. for aperiod of 0.5 hours or longer, the second heat treatment being conductedat a temperature of 90° C. to 140° C. for a period of 0.5 hours to 10hours, the first heat treatment being conducted at a lower temperaturethan the second heat treatment, and the lead-base alloy grid forlead-acid battery being made under gravity casting system, die castingsystem, continuous casting system, or rolling system.
 10. A method forproducing a lead-base alloy grid for lead-acid battery, comprising heattreatment of a Pb—Ca—Sn alloy substrate containing 0.06% by mass or lessof calcium, the heat treatment being conducted in two steps, naturalaging being conducted before the first heat treatment, the first heattreatment being conducted at a temperature of 40° C. to 110° C. for aperiod of 0.5 hours or longer, the second heat treatment being conductedat a temperature of 90° C. to 140° C. for a period of 0.5 hours to 10hours, the first heat treatment being conducted at a lower temperaturethan the second heat treatment, and the lead-base alloy grid forlead-acid battery being made under gravity casting system, die castingsystem, continuous casting system, or rolling system.
 11. A method forproducing a lead-base alloy grid for lead-acid battery, comprising heattreatment of a Pb—Ca—Sn alloy composed of 0.02% by mass or more and lessthan 0.05% by mass of calcium, 0.4% by mass or more and 2.5% by mass orless of tin, 0.005% by mass or more and 0.04% by mass or less ofaluminum, and 0.002% by mass or more and 0.014% by mass or less ofbarium, the remainder being composed of lead and unavoidable impurities,the heat treatment being conducted in two steps, natural aging beingconducted before the first heat treatment, the first heat treatmentbeing conducted at a temperature of 40° C. to 110° C. for a period of0.5 hours or longer, the second heat treatment being conducted at atemperature of 90° C. to 140° C. for a period of 0.5 hours to 10 hours,the first heat treatment being conducted at a lower temperature than thesecond heat treatment, and the lead-base alloy grid for lead-acidbattery being made under gravity casting system, die casting system,continuous casting system, or rolling system.
 12. A method for producinga lead-base alloy grid for lead-acid battery, comprising heat treatmentof a Pb—Ca—Sn alloy composed of 0.02% by mass or more and less than0.05% by mass of calcium, 0.4% by mass or more and 2.5% by mass or lessof tin, 0.005% by mass or more and 0.04% by mass or less of aluminum,0.002% by mass or more and 0.014% by mass or less of barium, and atleast one element selected from, the group consisting of 0.005% by massor more and 0.070% by mass or less of silver, 0.01% by mass or more and0.10% by mass or less of bismuth, 0.001% by mass or more and 0.05% bymass or less of thallium, the remainder being composed of lead andunavoidable impurities, the heat treatment being conducted in two steps,natural aging being conducted before the first heat treatment, the firstheat treatment being conducted at a temperature of 40° C. to 110° C. fora period of 0.5 hours or longer, the second heat treatment beingconducted at a temperature of 90° C. to 140° C. for a period, of 0.5hours to 10 hours, the first heat treatment being conducted at a lowertemperature than the second heat treatment, and the lead-base alloy gridfor lead-acid battery being made under gravity casting system, diecasting system, continuous casting system, or rolling system.
 13. Amethod for producing a lead-base alloy grid for lead-acid battery,comprising heat treatment of a Pb—Ca—Sn alloy composed of 0.02% by massor more and less than 0.05% by mass of calcium, 0.4% by mass or more and2.5% by mass or less of tin, 0.005% by mass or more and 0.04% by mass orless of aluminum, and 0.002% by mass or more and 0.014% by mass or lessof barium, the remainder being composed of lead and unavoidableimpurities, the heat treatment being conducted in two steps, the firstheat treatment being conducted at a temperature of 40° C. to 110° C.,the second heat treatment being conducted at a temperature of 90° C. to140° C., the first heat treatment being conducted at a lower temperaturethan the second heat, treatment, and the lead-base alloy grid forlead-acid battery being made under gravity casting system, die castingsystem, continuous casting system, or rolling system.
 14. A method forproducing a lead-base alloy grid for lead-acid battery, comprising heattreatment of a Pb—Ca—Sn alloy composed of 0.02% by mass or more and lessthan 0.05% by mass of calcium, 0.4% by mass or more and 2.5% by mass orless of tin, 0.005% by mass or more and 0.04% by mass or less ofaluminum, and 0.002% by mass or more and 0.014% by mass or less ofbarium, the remainder being composed of lead and unavoidable impurities,the heat treatment being conducted in two steps, natural aging beingconducted before the first heat treatment, the first heat treatmentbeing conducted at a temperature of 40° C. to 110° C. for a period of0.5 hours or longer, the second heat treatment being conducted at atemperature of 90° C. to 140° C. for a period of 0.5 hours to 10 hours,the first heat treatment being conducted at a lower temperature than thesecond heat treatment, and the lead-base alloy grid for lead-acidbattery being made under gravity casting system, die casting system,continuous casting system, or rolling system.
 15. A method for producinga lead-base alloy grid for lead-acid battery, comprising heat treatmentof a Pb—Ca—Sn alloy composed of 0.02% by mass or more and less than0.05% by mass of calcium, 0.4% by mass or more and 2.5% by mass or lessof tin, 0.005% by mass or more and 0.04% by mass or less of aluminum,and 0.002% by mass or more and 0.014% by mass or less of barium, theremainder being composed of lead and unavoidable impurities, the heattreatment being conducted in two steps, natural aging being conductedbefore the first heat treatment, the first heat treatment beingconducted at a temperature of 40° C. to 110° C., the second heattreatment being conducted at a temperature of 90° C. to 140° C., thefirst neat treatment being conducted at a lower temperature than thesecond heat treatment, and the lead-base alloy grid for lead-acidbattery being made under gravity casting system, die casting system,continuous casting system, or rolling system,
 16. A method for producinga lead-base alloy grid for lead-acid battery, comprising heat treatmentof a Pb—Ca—Sn alloy composed of 0.02% by mass or more and less than0.05% by mass of calcium, 0.4% by mass or more and 2.5% by mass or lessof tin, 0.005% by mass or more and 0.04% by mass or less of aluminum,0.002% by mass or more and 0.014% by mass or less of barium, and atleast one element selected from the group consisting of 0.005% by massor more and 0.070% by mass or less of silver, 0.01% by mass or more and0.10% by mass or less of bismuth, 0.001% by mass or more and 0.05% bymass or less of thallium, the remainder being composed of lead andunavoidable impurities, the heat treatment being conducted in two steps,the first heat treatment being conducted at a temperature of 40° C. to110° C., the second heat treatment being conducted at a temperature of90° C. to 140° C., the first heat treatment being conducted at a lowertemperature than the second heat treatment, and the lead-base alloy gridfor lead-acid battery being made under gravity casting system, diecasting system, continuous casting system, or rolling system.
 17. Amethod for producing a lead-base alloy grid for lead-acid battery,comprising heat treatment of a Pb—Ca—Sn alloy composed of 0.02% by massor more and less than 0.05% by mass of calcium, 0.4% by mass or more and2.5% by mass or less of tin, 0.005% by mass or more and 0.04% by mass orless of aluminum, 0.002% by-mass or more and 0.014% by mass or less ofbarium, and at least one element selected from the group consisting of0.005% by mass or more and 0.070% by mass or less of silver, 0.01% bymass or more and 0.10% by mass or less of bismuth, 0.001% by mass ormore and 0.05% by mass or less of thallium, the remainder being composedof lead and unavoidable impurities, the heat treatment being conductedin two steps, the first heat treatment being conducted at a temperatureof 40° C. to 110° C. for a period of 0.5 hours or longer, the secondheat treatment being conducted at a temperature of 90° C. to 140° C. fora period of 0.5 hours to 10 hours, the first heat treatment beingconducted at a lower temperature than the second heat treatment, and thelead-base alloy grid for lead-acid battery being made under gravitycasting system, die casting system, continuous casting system, orrolling system.
 18. A method for producing a lead-base alloy grid forlead-acid battery, comprising heat treatment of a Pb—Ca—Sn alloycomposed of 0.02% by mass or more and less than 0.05% by mass ofcalcium, 0.4% by mass or more and 2.5% by mass or less of tin, 0.005% bymass or more and 0.04% by mass or less of aluminum, 0.002% by mass ormore and 0.014% by mass or less of barium, and at least one elementselected from the group consisting of 0.005% by mass or more and 0.070%by mass or less of silver, 0.01% by mass or more and 0.10% by mass orless of bismuth, 0.001% by mass or more and 0.05% by mass or less ofthallium, the remainder being composed of lead and unavoidableimpurities, the heat treatment being conducted in two steps, naturalaging being conducted before the first heat treatment, the first heattreatment being conducted at a temperature of 40° C. to HOC the secondheat treatment being conducted at a temperature of 90° C. to 140° C.,the first heat treatment being conducted at a lower temperature than thesecond heat treatment, and the lead-base alloy grid for lead-acidbattery being made under gravity casting system, die casting system,continuous casting system, or rolling system.